Substantial research effort has been expended trying to understand how behavior comes to be acquired as the result of exposure to events in the environment. This is because it is generally believed that most of the components of an individual's behavioral repertoire are learned through that exposure. Several general laws of behavioral adaptation have emerged such as: "the consequences of a behavior strongly influence its subsequent rate", "a neutral stimulus paired with a biologically significant one comes to control an analogous behavior", and "discriminably different stimuli associated with different outcomes come to control different behaviors". Much of the research in psychology can be seen as detailing the conditions under which these laws hold and the factors which influence them. In Kuhn's (1970) terms, this is "normal" science. When a fixed interfood interval is segmented into a series of discrete stimuli, chronic responding occurs to the stimuli denoting the segments of the last half of the interval (Palya, 1985). This behavior is seemingly anomalous in that discriminable stimuli, differentially associated with nonreinforcement, maintain chronic responding. Two experiments will examine how to best characterize the mechanism underlying this responding. Both experiments will be derived from a simple, fixed interfood interval segmented into time periods, each of which can be designated by a different key color. Experiment 1 will examine the appropriateness of various nonserial mechanisms as explanations for the responding to antecedent stimuli. Nonserial mechanisms are those which are not based on a formerly neutral stimulus coming to function like a biological reinforcer. Experiment 2 will assess the applicability of serial mechanisms, such as higher-order conditioning, which are based on neutral stimuli which come to function as reinforcers.